The present disclosure relates to materials testing, and more specifically, to verifying a purported composition of material in a solid metal object.
Precious metal objects, such as precious coins, bullion bars, or other precious metal objects may be certified or labeled as having a particular composition of material. For example, a gold coin or bar may be certified as having a particular karat rating, indicating that the object is composed of a specific percentage of gold. A coin labeled as “24 karat” is purportedly composed of over 99% pure gold. However, in some instances, while certified as having a particular composition of precious metal, in reality, the coin or bar may actually be composed of an exterior layer of precious metal hiding relatively low cost metal in the interior of the coin or bar.
For example, an unscrupulous person could fabricate a fake 10 oz gold bullion bar that, in reality, includes a 6.0 oz slug of tungsten clad with 4.0 oz of gold. The person could then imprint the design and mint signatures from a reputable gold supplier on the bar to mislead consumers as to the actual value of the item. At today's price of gold at around $1200 per ounce verses the price of tungsten at around $30 per kilogram, a consumer would be cheated out of $7200.00 of gold.
This interior metal slug may be difficult to detect by visual, dimensional/weight or surface testing. For example, tungsten and gold have a have a similar density (e.g. Tungsten has a density of approximately 19.35 g/cm3 while Gold has a density of approximately 19.32 g/cm3, a difference of approximately 0.16%). Thus, a supposedly gold coin or bar that includes a slug of tungsten will be nearly identical to a coin or bar made entirely of gold. Additionally, with computer aided manufacturing technology, it has become cheaper and easier to produce these type of fake coins and bars.
Known methods for verifying the purity of a coin or bar have consisted of visual verification by inspection of a drilled or cut sample of material from the object. Additional known methods for verifying consisted of melting point comparison by melting a sample of the material, and X-ray or ultrasound analysis. However, these methods are undesirable as they may result in damage to the original coin or bar, devalue the object, require specialized equipment, are cost prohibitive, and are time consuming. Accordingly, an improved method of verifying the purity of a coin or bar is desirable.